Conductive printed plastic strips

ABSTRACT

Electrically conducting printable webs of plastic have upper and lower sides, at least of the sides is provides with a primer layer for printing pretreatment formed using a substance selected from the group consisting of polyurethanes, acrylates, polyester resins with isocyanates, and combinations thereof, on which another layer containing an electrically conducting organic polymer is coated.

The present invention relates to electrically conducting printable websof plastic, processes for the preparation of electrically conductingprintable webs of plastic, and a binder by means of which electricallyconducting organic polymers can be applied to plastic sheets.

For reasons of explosion protection and electromagnetic shielding anddue to the increased demand for electroluminescent displays, LCDs andtouch screens, electrically conducting surfaces are increasingly gainingimportance because they can prevent electrostatic charging. The focus ofinterest is shifting more and more to electrically conducting plasticsurfaces.

The conventionally used plastics have a high resistance which may be inthe range of 10¹⁵ Ohm/□. In order to increase the conductivity ofplastics, especially of plastic sheets, metallic screen printing inks,carbon paints or wire gauze are used. However, if transparent surfacesare required, this is not possible since the surface would be no longertransparent eventually.

Therefore, to prepare transparent, electrically conducting surfaces,plastic sheets are sputtered with metal oxide layers in an expensiveprocess under ultrahigh vacuum. Usually, indium tin oxide (ITO) is usedfor this purpose.

However, these sputtered layers cannot be printed afterwards since theprinting inks fail to adhere to the metal oxide layer satisfactorily. Onthe other hand, if layers already printed are to be sputtered, there isa risk that volatile components of the printing inks are vaporized inthe ultrahigh vacuum necessary for sputtering.

Due to the use of ultrahigh vacuum, sputtering processes are veryexpensive. Further, sputtered layers exhibit a change in resistance uponmechanical and/or thermal deformation of the surface.

The use of the heavy metal oxides in sputtered layers involves a dangerfor humans and the environment both in production and in application.

The object of the invention has been to provide electrically conductiveplastic surfaces which can be printed on with a particularly goodadhesion and have improved surface properties, and processes for thepreparation of such plastic surfaces in which the use of ultrahighvacuum and heavy metals is eliminated.

Surprisingly, the object of the invention is achieved by electricallyconducting printable webs of plastic having the features of claim 1, bypreferred embodiments according to claims 2 to 6, electricallyconducting printed webs according to claim 7, a preparation processaccording to claim 9, and the use of the electrically conductingprintable webs of plastic according to claim 14. Claims 10 to 13 arepreferred embodiments of the process.

The electrically conducting printable webs of plastic according to theinvention have upper and lower sides, at least one of said sides beingprovided with a primer layer for printing pretreatment, comprising asubstance selected from the group consisting of polyurethanes,acrylates, polyester resins with isocyanates or combinations thereof, onwhich another layer containing an electrically conducting organicpolymer is coated.

These plastic webs are advantageous, in particular, when an electricallyconducting surface is needed for reasons of explosion protection orelectromagnetic shielding, or for printing with electroluminescentpastes. In addition, these plastic webs do not exhibit a significantchange in resistivity upon being deformed.

Preferably, the plastic webs are made of polyethylene, polycarbonate,polyacrylate, polyester, polypropylene, poly(vinyl chloride) orcopolymers thereof.

The primer layer for the electrically conducting printable webs ofplastic are formed by a primer made of polyurethanes, acrylates,polyester resins with isocyanates. Particularly preferred components ofthe primer are acrylate copolymers of the Neocryl series ofPolyvinyl-Chemie Holland N.V. (Neocryl XK90, XK11, BT26, A-1052),Halloflex 202 available from ICI (vinyl acrylate copolymer), NeopacE-130 (polyurethane-acrylic copolymer), Viclan VL805 (PVDC), DynapolL206 (polyester), Elecond PQ50B (acrylate), Alberdingk APU1060 and U910(polyethylene-polyurethane copolymers), Saran F-310 (PVDC), AlberdingkAPU1014, Aquacote 287/4 (styrene acrylate), Neorez R-970, R-973, R-974,R-986, R-940, R-972, optionally together with Xama(tris(N-aceridinyl)ethane), poly(oxy-p-phenylenesulfonyl-p-phenylene) ofthe PES series available from Deutsche ICI GmbH (PES 2000, PES 124G, PES124S, PES 215G) , Vylon 103, Vylon 240, Pioloform BL 18, PolyDisB/300LF,Plexigum M890, Vital PE-2200, Ucar Vinyl VMCH, Melinex 525, NeocXK11,NeocA1052, Cariflex TR1102, Clarene R-20 and Clarene L-6. The primerlayer serves as a printing pretreatment and mediates the adhesion of theinks, paints, pastes or the like, applicable by various printingmethods, which would otherwise perhaps not exhibit sufficient adhesionon the plastic webs, especially when deformed.

In this connection, a good adhesion means that the printed electricallyconducting webs of plastic according to the invention will achieve a GTvalue of between 0 and 3, preferably between 0 and 2, especially between0 and 1, in a cross-hatch adhesion test according to DIN 53 151 or ASTMD 3002 or ASTM D 3359.

The GT value indicates how strongly a printed structure or the likeadheres to the surface. GT values are a measure for the adhesion of theprinted structure to the surface and range from 0 to 5. A value of 5indicates that an almost complete removal of the printed structure hasoccurred in the test whereas a GT value of 0 means that no printedstructure has been removed. Thus, low GT values mean a good adhesion ofthe printed structure to the surface.

As said electrically conducting organic polymer, there are used, inparticular, polyamidines, polyacetylenes, polypyrroles, polythiophenes,free-radical containing salts and combinations thereof. Suitablematerials include N-n-propyl-i-quinolinium, available as OS-CON fromSanyo (Japan), polyanilines available under the designation Incoblendfrom Zipperling-Kessler (Germany), polythiophenes available under thetrade name Hostaphan RN 12 from Hoechst (Germany), polyanilinesavailable under the designation CP EX-1 available from Hexcel (USA), andthe products of Ciba-Geigy (Switzerland) available under the designationTEC.

“Free-radical containing salts” means those compounds, in particular, inwhich a plastic material has been converted to a free-radical containingstate by doping, for example, with Br₂ or I₂.

The layer containing the electrically conducting organic polymeroptionally contains a binder whereby the adhesion to the primer layercan be improved. In particular, the ratio of electrically conductingorganic polymer to binder can be varied in such a way, that besides verysmall resistances, resistances in the range around 10⁶ Ohm/□ havingantistatic properties can also be achieved.

It is advantageous to use transparent polymers because mechanically andthermally deformable, transparent, printable, electrically conductingplastic webs are thus obtained which have not been available to date inthis form.

It is particularly advantageous to use the plastic web according to theinvention in the fields where transparency of the plastic surface isnecessary, for example, as a display in electronic equipment.

These printable webs of plastic can be printed or coated with, forexample, printing inks, paints, hard lacquers, electroluminescent screenprinting pastes or liquid crystals. In addition, the printing and/orcoating can be effected on both sides irrespective of whether the layercontaining the electrically conducting organic polymer is applied on oneor both sides.

As the binders for applying the electrically conducting organic polymer,artificial resins or artificial-resin-like substances, such aspoly(vinyl chloride) latexes, poly(methyl methacrylate) latexes,polyurethane dispersion, poly(vinyl acetate) or poly(vinyl alcohol), areparticularly suitable.

The process according to the invention for the preparation ofelectrically conducting printable webs of plastic involves theapplication of a primer to form a primer layer for printingpretreatment, and the application of another layer containing anelectrically conducting organic polymer.

The process is characterized, in particular, by the application of theconductive coating under normal pressure and by the avoidance of heavymetals.

Particularly suitable are methods in which the primers forming theprimer layer are applied by coating techniques such as reverse roll,knife or gravure coating.

For applying the conductive organic polymer, in particular, aqueous ororganic solutions or mixtures thereof are suitable, wherein alcohols,ketones, heterocycles or combinations thereof, in particular, aresuitable as solvents for the solution. Optionally, the polymer isapplied together with a binder.

The structure of the plastic web according to the invention and itspreparation are illustrated in the following Examples.

EXAMPLE 1

A biaxially drawn Mylar A type polyester sheet (DuPont) is coated withan acrylate primer diluted in acetone by a reverse-roll method. Thesubsequent drying is performed at 100° C., at a web speed of 3 m/min anda dryer length of 4 m. Onto the primer layer thus obtained, an aqueoussolution comprising 180 g of Baytron P (1.3%polyethylenedioxythiophenepolystyrenesulfonate), 15.4 g of Impranil 85UD, 6.5 g of N-methylpyrrolidone, 39.0 g of isopropanol, 2.1 g ofepoxysilane A 187 and 16 g of sorbitol (30% in H₂O) is coated, also by areverse-roll method. The drying is performed at 115° C. in a dryerhaving a length of 4 m at a speed of 5 m/min, followed by a protectiveprinting based on polyacrylate under UV irradiation of 800 mJ/cm² in ascreen-printing method (100 mesh T screen).

EXAMPLE 2

Solvent-containing or aqueous formulations containing conductive organicpolymers are coated onto 250 μm polycarbonate sheet (Lexan) using aknife-coating method with subsequent multiroll drying.

The knife-coating method is characterized by a deposition of excesscoating solution which is dosed to the intended coating quantity by a#50 wire knife coater.

The coating rate is 10 m/min.

In a subsequent multizone drying process, the conductive polymer layeris dried (2 m length, 10 m/min) at a temperature of 120° C. in the firstdrying segment (2 m length) and of 130° C. in the second drying segment.The sheet thus obtained (resistance 104-105 Ω/□) is printed withMarastar ink (Marabu).

EXAMPLE 3

A layer containing a conductive organic polymer and having a resistanceof about 3000 Ω/□ is bonded to PET with a good adhesion and is printablewith solvent-based screen-printing methods. The structure forelectroluminescence is as follows.

1. base (PET Mylar, Melinex or polycarbonate (Lexan), 250 μl);

2. conductive layer (by analogy with Example 1 or 2);

3. electroluminescent layer (e.g., 7151 E, DuPont), drying at 120° C.(air drying, 5 min in furnace);

4. second insulation paint layer (e.g., 7153 E, DuPont), drying at 120°C. (air drying);

5. silver conductive paint (e.g., 7145 L, DuPont), drying at 120° C.(air drying in furnace).

Contacting after drying, drying 110 V, 400 Hz.

EXAMPLE 4

A 3000 Ω/□ sheet prepared as in Example 3 was printed with DuPont pastesaccording to directions (Luxprint), also, embossed to a depth of 4 mm,male mold 70° C., female mold room temperature (25° C.).

A polyester sheet, sputtered with ITO (100 Ω/□), was subjected to thesame printing and embossing procedures. Both were subjected to a liftingtest (Böck tester, 5 N sensor). With the ITO sheet, rupture occurredafter about 100 lifts (dimming of the EL lamp over the print). The 3000Ω/□ sheet of the invention exhibited its complete illuminating powereven after 1.7 million lifts.

EXAMPLE 5

A polyester sheet (Mylar D, 175 μm) was coated with a conductive polymeraccording to the above mentioned formulation. A 175 μm Mylar D was alsotreated with the above mentioned primer and then provided with aconductive formulation under the same conditions as the untreated MylarD base. Both samples were printed with a screen-printing ink of Marabu,Marastar SR (100 mesh T screen, drying 2 min at 70° C.). Then, across-hatch adhesion test according to DIN 53 151 or ASTM D 3002 wasperformed. The printing of the polyester which had only been treatedwith the conductive polymer resulted in a GT of 4 to 5 (almost completebreaking off) whereas good to very good adhesion values (GT 0 to 1) wereachieved by the additional primer coating.

What is claimed is:
 1. Electrically conducting printable webs of plastichaving (a) upper and lower sides, at least one of said sides beingprovided with (b) a primer layer for printing pretreatment, comprising asubstance selected from the group consisting of polyurethanes,acrylates, polyester resins with isocyanates, and combinations thereof,on which is coated (c) another layer containing, in the absence of heavymetals, an electrically conducting organic polymer.
 2. The electricallyconducting printable webs of plastic according to claim 1, characterizedin that said webs are made of polyethylene, polycarbonate, polyacrylate,polyester, polypropylene, PVC or copolymers thereof.
 3. The electricallyconducting printable webs of plastic according to claim 1, characterizedin that said electrically conducting organic polymer is selected fromthe group of polyacetylenes, polypyrroles, polythiophenes, free-radicalcontaining salts and combinations thereof.
 4. The electricallyconducting printable webs of plastic according to claim 1, characterizedin that said layer containing the electrically conducting organicpolymer additionally contains a binder.
 5. The electrically conductingprintable webs of plastic according to claim 1, characterized in thatsaid electrically conducting organic polymer, said binder and/or saidprimer layer are transparent.
 6. The electrically conducting printablewebs of plastic according to claim 1, characterized in that they can beprinted or coated with screen printing inks, paints, luminescent pastes,liquid crystals or hard lacquers.
 7. Electrically conducting printedwebs or plastic, obtainable by printing the electrically conductingprintable web of plastic according to claim 1 with inks, paints and/orpastes.
 8. The electrically conducting printed webs according to claim7, characterized in that said web exhibits a cross-hatch adhesion testvalue according to DIN 53 151 or ASTM D 3002 of from 0 to 3.